Adhesive coated sheets and method of manufacture



Aug. 9, 1966 H. R. DALTON 3,265,555

ADHESIVE COATED SHEETS AND METHOD OF MANUFACTURE Filed April 10, 1962INVENTOR" Z6 flaw/.2: R. $44 TON TT RNEY required usable tackiness.

United States Patent O 3,265,555 ADHESIVE COATED SHEETS AND METHOD OFMANUFACTURE Harold R. Dalton, Rydal Road, Jenkintown, Pa. Filed Apr. 10,1962, Ser. N 0. 186,386 18 Claims. (Cl. 161-161) This invention relatesto the coating art and more especially it relates to the coating ofsheet or web material whose dimensional stability is subject to changeduring, or as a result of, the coating operation.

In certain of the arts, particularly in the art of adhesive coating uponpaper, the adhesive film upon drying tends to shrink in greaterproportion to the paper. Consequently, when the coating material issubjected to the usual drying heat to form it into a film, and since thecoating material usually has a different shrinking characteristic fromthat of the paper, the differential characteristics of the paper andcoating tend to cause the paper to curl or otherwise dimensionallydistort. This problem is particularly noticeable where the coatingmaterial is a gum, glue or similar moistenable adhesive. Ordinarily,when such glue coating is applied in liquid form to a paper or similarporous backing, the coating when dried is a continuous film and thesurface continuity thereof increases the tendency of the paper to curl.

This problem of curling is so pronounced in the gum coating art that ithas been necessary heretofore to subject the gum or glue coating to amechanical breaking operation. Thus, in the manufacture of gummed paperin continuous lengths or sheets which are subsequently to be cut intosealing tapes, labels, stamps, etc., it is customary to process thegummed sheet in a breaking machine before it is subjected to thesubsequent processing operations such as slitting, cutting, printing,punching, etc. In other words, it has been found necessary to break orcrack the glue or gum layer into sections so as to effect adiscontinuous film and thereby reduce the curling effect. The fihnbreaking operation is employed to produce a finishedgummed sheet thathas as closely as possible the same handling properties as the originaluncoated paper, fabric or foil, and also to modify the gummed film sothat it will readily accept water or other softening liquid when the gumcoating is to be moistened to give it the The equipment for mechanicallyaccomplishing the film breaking is well known in the art, and for thatpurpose reference may be had to the periodical publication entitledPaper, Film and F-oil Converter, May 1957, page 27. This machine, whichis used quite generally, consists essentially of unwind and rewindstands between which are located two sharp-edged breaker bars or edgesplaced at an angle of approximately 45 degrees to the length of thesheet and at approximately 90 degrees to each other. The ungummedsurface of the paper, fabric or foil is forced against the sharp edgesof the breaking bars to crack the adhesive coating, which for examplemay be bone glue, hide glue, dextrine, gum arabic, polyvinyl alcoholprany other well known adhesive which is intended to be subsequentlymoistened to render it tacky.

The film breaking operation entails considerable waste of paper or othermaterial that is to be gummed, especially since the sheet material isusually coated in a relatively high speed sheet feeding operation. Sincethe paper or similar sheet material must be held taut against, orotherwise pressed against and deflected around, the sharp edges of thebreaking bars, there is always the possibility of the sheet rupturing ortearing, and a considerable length of paper is ruined before the coatingmachine can be brought to rest. Furthermore, since the sharp-edgedbreaker bars are in tight pressing engagement with the uncoated side"ice of the sheet, the mechanical rubbing or scraping may affect thesurface characteristics of that uncoated side so as to render itunsatisfactory for subsequent printing, drawing or other operations tobe performed on the un coated side. The above difficulties are, ofcourse, greatly increased in proportion to the thinness or fragility ofthe sheet which is being gummed or coated, thus limiting the use of thecoating and breaking equipment to sheets in excess of a predeterminedminimum thinness.

I have found that the above noted and other difficulties can be avertedby eliminating the usual mechanical fihn breaking and by efiecting thebreakage of the film by what may be termed a physio-chemical actionwithin the fihn itself. Accordingly, one of the principal objects of thepresent invention is to provide a backing sheet with a novel coatingwhich is broken to render the coating discontinuous but withoutrequiring external mechanical breaking force. Another object is toproduce a broken or discontinuous film without marring or physicallydisturbing the uncoated surface of the backing sheet which carries thefihn on its opposite surface.

Another object is to provide a broken or discontinuous surface filmwhich has fracture or breakage lines of greater number per unit areathan has been possible with fihns broken with the usual mechanicalbreaking operations.

Another object is to provide a broken or surface discontinuous adhesivefilm wherein the fracture or breakage lines are produced in a greaternon-statistical array than is possible with the breaking effected byphysical breaker bars or the like.

A further object is to provide a process of coating a backing sheet ofpaper, film, foil or the like with a broken adhesive film wherebylighter weight stock can be used for the backing than has beenpracticable heretofore.

A feature of the invention relates to a novel coating batch forproducing a fractured or broken surface film on a flexible backingsheet, which batch has incorporated therein a material that effects thefilm breakage by an inherent explosive or disruptive action, but withoutdestroying or reducing the interfacial adhesive force between thebacking sheet and film.

Another feature relates to a gummed paper or the like which isparticularly free from curling or similar dimensional distortion, whileat the same time possessing a high order of receptivity to water orsimilar moistening agent when the paper is subsequently being treated torender it tacky.

. A "further feature relates to an improved laminated paper or cardboardproduct and also to an improved such product of the corrugated kind.

Other features and advantages not particularly enumerated will beapparent after a consideration of the following detailed descriptionsand the appended claims.

In the drawing,

FIG. 1 is a top plan view in schematic form showing the mechanical fihnbreaking equipment heretofore considered necessary for fihn breakage;

FIG. 2 is a side perspective view of FIG. 1;

FIG. .3 is a drawing of a photomicrograph taken of an adhesive coatedpaper showing the film fracture lines produced by the conventionalmechanical breaking mechanisrn;

FIG. 4 is a drawing of a photomicrograph of an adhesive coated paperwherein the broken adhesive film is prepared according to one embodimentof the invention;

FIG. 5 is a drawing of a photomicrograph of an adhesive coated paperwherein the broken adhesive film is prepared according to anotherembodiment of the invention;

3 FIG. 6 shows an improved laminated product embodying the invention;

FIG. 7 shows an improved cocrugated product embodying the invention.

Referring to FIGS. 1 and 2, the basic parts of the conventionalmechanical film breaking equipment are schematically shown, comprising,for example, the un-- wind roll 10 from which the previously driedgummed.

paper 11 is unrolled and rewound on the rewind roll 12. Located betweenthe two rolls are the usual adhesive film breaker bars 13, 14 which areusually at an angle of 45 degrees to each other and which are held inpressed engagement with the ungummed surface of the paper 11, asindicated schematically by'the offset rollers 15, 16 adjacent the bars13, 14 as shown. In other words, the paper is held taut against thebreaker bars. As a result of this mechanical breaking, the previous gumcoating on the paper 11 which had a continuous surface is mechanicallybroken or fractured. In some cases, a third breaker bar 17 and offsetroller 17a extends parallel to the sheet width. FIG. 3 shows amagnification (fifty times) of a portion of such a sheet after breakageof the gummed film. It will be observed that the fracture lines are inall cases roughly linear and define roughly triangular areas ofcomparatively regular statistic shape; Because of the physical nature ofthe breaking operation, it is not practicable to decrease the size ofthe areas bounded by the fracture lines even though such a reduction hasdecided advantages. One of the advantages in decreasing the bounded areabetween fracture lines is the improvement in water absorption propertiesof the dried film.

I have found that the breakage of the gum film can be effected byincorporating into the gumming material, prior to its application to thepaper 11, a finely divided solid chemical having the property ofproducing gas when heated to a certain temperature within the usualdrying range to which the gummed paper is subjected, more specificallywithin the range of temperatures used in commercial drying ovens whichis from 220 degrees F. to 500 degrees F. While the present invention isnot limited to any particular solid chemical gassing agent for the abovebreakage purpose, the following nitrogenous agents have been foundsatisfactory for that purpose:

4,4 Oxybis (benzenesulfonyl semicarbazide) 4,4 Oxybis (benzenesulfonylhydrazide) Azodicarbonamide Trihydrazino-sym-triazine N,N' dimethyl N,Ndinitrosoterephthalamide Barium azodicarboxylate Bis-benzenesulfonylhydrazide Of the above, the azodicarbonamide is particularlyadvantageous since, after the decomposition and gas releasing, no traceof the'chemical is left in the gum coating. While the above are given asillustrative of suitable chemical gassing agents, other such agents maybe used, the prerequisite being that they be solid at room temperature,decompose at a temperature within the working range of the gummingequipment, produce a suflicie nt amount of gas when used in smallpercentages to accomplish the desired film breakage, and that both thegassing agent and the decomposition products be nontoxic andnon-hazardous to handle.

If any one of the above gassing agents is dispersed with a waterremoistenable adhesive in an amount of from approximately 0.5 percent to10 percent of the dry weight of the adhesive, applied to paper or othersheet material by any one of the well known methods such as rollcoating, doctor blade coating, knife coating, etc., in an amount to givethe usually applied weight or thickness common in industry, i.e. fromtwo pounds totwenty pounds (24" x 3 "500), and dried in an oven at theproper temperature and lineal speed, it is found that the entire driedadhesive film will be broken with random 3 comparative similar results.

fracture lines, the breaking seemingly being caused by the individualdispersed solid particles of gassing agent decomposing and producing agas which will crack the film before leaving the area within which itwas entrapped.

The dextrine and water were mixed with a high speed mixer until thedextrine was dissolved. T-he azodicarbonamide was then added and.mechanical agitation continued for about fifteen minutes. The liquidadhesive mixture was applied to a sixteen pound bond paper with a rollcoater to give a dried coating weight of fifteen pounds (24" x 36500).The coated paper was dried at a temperature of 350 degrees F. The-sheetlaid flat after cooling and its surface was Well broken, as shown inFIG. 4. The same solution was applied to kraft paper (sixty pound 24" x3 "-500) and drafting cloth with Example 2 This example utilizesdimethyl dinitrosoterephthalamide as a gassing agent using mechanicaldispersion.

Pounds Stein Hall gumming grade dextrine 200.0 Water 160.0 Dimethyldinitrosoterephthalamide 5.0

The dispersion was prepared and coated as indicated in Examplel. Thecoated paper was partially dried at a temperature of 200 degrees F. andthen passed over a polished sheet drum, gummed face out, heated to 350F. The sheet laid fiat after cooling and its surface was well brokensimilar to that of FIG. 4.

Example 3 This example utilizes azodicarbonamide chemically dispersed ina dextrine solution, using physio-chemical dispersion.

Triton X-l00 (Rohm & Haas dispersing agent;

alkyl aryl polyether alcohol) 2.0

' The dextrine and water were mixed with a high speed mixer until thedextrine was dissolved. The Triton X.- 100 was added to theazodicarbonamide, a little water added (1 pound) and mixed until asmooth paste was formed:- another pound of Water was added, and then thedispersion transferred to the dextrine solution while the latter wasbeing agitated. The agitation was continued for about fifteen minutes.The mixture was applied to paper as in Example 1. The sheet laid flatafter cooling and its surface was well broken; a finer structure of thebroken adhesive layer was obtained compared to Example 1, as shown inFIG. 5.

Example 4 This example utilizes azodicarbonamide mechanically dispersedin an animal glue solution.

Pounds Darling animal glue, g 120.0

Naphtha bone glue 80.0

Pounds Water a 185.0 Azodicarbonamide 4.0

, Soak the glue in water until swollen and then heat to 150 degrees F.Add the azodicarbonamide and agitate for fifteen minutes with a highspeed mixer. The liquid adhesive was applied to a fifth pound (24" X36"500).

clay coated paper with a blade coater to give a direct coating weight ofeighteen pounds (24" X 36-500). The coated paper was dried at atemperature of 350 degrees F. The sheet laid flat after cooling and itssurface waswell broken. The same, solution was applied to ametal foillaminated paper with similar results.

Example 5 This example utilizes dimethyl dinitrosoterephthalamide with asynthetic adhesive polyvinyl alcohol.

Pounds Polyvinyl alcohol (Dupont 52-22) 100.0 Water 800.0 Dimethyldinitrosoterephthalamide 4.0

Example 6 This example utilizes bis-benzenesulfonyl hydrazidemechanically dispersed in a kraft sealing tape gumming solution.

Pounds Darling glue, 120 g 180.0 Water 175.0 Bis-benzenesulfonylhydrazide 14.0

The dispersionwas prepared and coated as indicated in Example 2 and theresults were similar to those obtained in that example.

. While the examples given contain only water as a solvent, variousother materials may be used along with the water to modify the filmproperties of the adhesive during the drying process to develop thedesired random breakage lines, certain fineness of grain or crackle,certain cellular structure, etc. Materials that are suitable for thispurpose are the glycol ethers, high boiling alkylene amines,alkanolamines and alcohols, etc. Also, the adhesive film itself may.consist of more than one type of adhesive and certain softening agentslike glycerine,

' glycols, sorbitol, etc., or other additives, such as pyrophosphates,gluconic acid, pigments, fillers, etc., may be a part of theformulation. Other'modifying agents to impart anti-blocking propertiessuch as polyvinyl methyl ether, polyvinyl acetate, polyacrylic acid,polyvinyl acetatemaleic anhydride copolymer, polyethylene glycols, etc.,may also be used in the gumming formulation.

While particular chemicals, temperatures and drying times have beenmentioned hereinabove, it will be understood that such' are given purelyby way of illustration and-not by way of limitation. Furthermore, whilethe invention finds its primary utility in the manufacture of gummed orglued sheets, in certain of its aspects the invention is equally welladapted to other kinds of coatings where it is desired to avoidmechanical breaking of the coating while producing such a coating with.a multiplicity of fracture lines arranged in a substantiallynon-statistical array so that the chances of forming a number ofindividually continuous fracture lines across the coated sheet aregreatly reduced.

While the invention has been described hereinabove as applied to thegumming of a single sheet or web, the invention also finds utility inthe manufacture of laminated sheets, composed of a plurality of sheetsof fibrous stock bonded together at adjacent faces by an intermediate,i.e. intervening, dried adhesive layer. In such laminated product theintermediate dried adhesive layer has a multiplicity of fracture linesoccurring in random array. Thus, FIG. 6 shows the invention applied totwo sheets of paper or cardboard which are laminated through theintermediary of glue or gum film which has been applied to either orboth of the opposed surfaces of the two liminated sheets 18, 19. Thisglue film 20 is prepared in accordance with the above disclosure. Afterbeing applied to one or both of the sheets, it is subjected to thedrying heat .above mentioned to cause the solid gas releasing particlesto disintegrate and fracture the bonding gum film between the sheets.This fracturing of the film increases the flexibility of the laminatedsheets without materially affecting the laminated bond therebetween.

FIG. 7 shows the invention applied to .a corrugated laminated productwherein the intermediate corrugated cardboard or paper portion 21 isbonded at its crests to the flat cardboard or paper sheets 22, 23. Thesesheets 22, 23 are provided with a film 24, 25 of the glue or gum abovedescribed, and when the sheets have been assembled in laminated arraywith the fiat sheets 22, 23 in contact with the crests of the corrugatedsheet 21, the assembly is subjected to the above noted drying heat tocause the film to become fractured as above described. This fracturingof the glue or gum film increases the resilient compressability of thecorrugated assembly without materially affecting the bond between thefiat sheets and the corrugated sheets.

One of the advantages of the fracturing method, according to theinvention, is that the gas releasing action is derived directly from thefracturing agent of the solid particles, these particles beingindividually and directly decomposed by the drying heat as distinguishedfrom the release of gas by chemical interaction of two or more chemicalswhich release such gas by ionic action. By such direct heatdisintegration of the solid particles, the production of the randomlyoccuring fracture lines in relatively close array is readily achieved.The invention is not limited to any particular degree of fineness ofthese particles, their fineness, of course, being correlated with thepsysical effect desired. Most of the gasing agents disclosed consist offine powder having a particle size of from 1 to 5 microns. However, whenmixedwith a water solution of a glue or gum, they form large.agglomerates which must be broken down by agitation or otherwise, as bymilling, into the individual particles or into small agglomerates togive the results desired. Thus, it will be noticed that mechanicalagitation for a short time produces fracture lines as in FIG. 4, whereasdispersing the particles more completely produces many more fracturelines per unit area as shown in FIG. 5.

It' will be understood that the term gum, .as used herein, is merelyillustrative of any well known moistenable adhesive which becomesusefully tacky when moistened with water or similar moistening agent. Itwill also be understood that the fracture lines referred to herein areof extremely thin or hairline form and are not visible except underrelatively high magnification.

7 What is claimed is: p

1. The method of providing over a flexible backing material a dryadherent film of a dryable, moist flowable adhesive coating composition,a coating of which has the undesirable tendency to shrink on drying andwhich is tacky when wetted and adherent when dry, and substantially toeliminate said tendency toward shrinkage, which method comprisesapplying to said backing material a moist, flowable adhesive ofsaid'coating composition containing dispersed therein a gas-providingsubstance which is stable therein at ordinary ambient conditions duringapplication and under elevated temperature employed to dry the appliedmoist film decomposes therein with release of gaseous decompositionproducts therefrom; and then subjecting the moist coating to an elevateddrying temperature sufiicient to dry it under the drying conditionsemployed and so simultaneously to decompose said gas-providing substanceand to enable the released gaseous products thereof to produce amultiplicity of fracture lines in the resulting dried adherent film ofthe adhesive material.

2. The method according to claim 1 in which said gas-providing substanceused has a decomposition temperature between 200 degrees F. and 500degrees F.

3. The method according to claim 1 in which said gasproviding substanceis incorporated in the coating composition as a comminuted solid.

4. The method according to claim 1 in which said gasproviding substanceis a member of the class consisting of oxybis benzenesulfonylsemicarbazide, oxybis benzenesulfonyl hydrazide, azodicarbonamide,trihydrazino-symtriazine, dimethyl dinitrosoterephthalamide, bariumazodicarboxylate, and bis-benzenesulfonyl hydrazide.

5. The method as claimed is claim 1, wherein said gasproviding substanceis azodicarbonamide.

6. The method according to claim 1, wherein said adhesive coatingcomposition contains as its adhesive constitutuent a member of the classconsisting of bone glue, hide glue, dextrine, gum 'arabic, and polyvinylalcohol.

7. The method of making a sheet coated with dried moistenable-adhesive,which method comprises preparing a dryable, moist, fiowable gummingbatch comprised of a moistenable-adhesive ingredient in a solventvehicle therefor and including dispersed therein solid particles of agas-providing substance whichis stable therein at ordinary ambientconditions and under elevated temperature used to dry a coating of saidbatch decomposes therein with release of gaseous decomposition productstherefrom; applying a suitable moist coating of said batch over abacking sheet; and then subjecting said moist coating on said sheet toan elevated drying temperature sufficient to dry it under the dryingconditions employed and so simultaneously to decompose saidgas-providing substance to enable the released gaseous products thereofto form said composition on the backing sheet into a driedmoistenable-adhesive film having a multiplicity of fracture lines.

8. The method as claimed in claim 7, wherein the solid particles of saidgas-providing substance are mechanically dispersed throughout thegumming batch before applying it to the backing sheet.

9. The method as claimed in claim 7, wherein a chemical dispersing agentis incorporated in the gumming batch.

10. The method according to claim 7, wherein the coated sheet is passedthrough a drying oven and said gas-providing substance has adecomposition temperature within the drying temperature range of saidoven.

11. The method of breaking a dried gum coating on a backing sheet, whichcomprises incorporating into the starting gum coating composition priorto applying it to said sheet a heat-decomposable coating-fracturingingredient, and after applying said coating composition to the.

sheet, heating it to decompose said ingredient thereby to fracture saidcoating by the resulting heat decomposition of said ingredient.

12. The method as claimed in claim 11, wherein said coating-fracturingingredient is a gas-providing substance which is stable at ordinaryambient conditions during application of said coating composition andunder elevated temperature decomposes therein with release of gaseousdecomposition products therefrom, and said heating of the coating is ata temperature sufficient to decompose said gas-providing substance torelease from it gas to effect said fracturing of the coating.

13. A coating batch for the manufacture of gummed sheets and the like,comprising a dispersion of a gum, a

solvent for the gum, and a gas-providing substance stable therein atordinary ambient conditions and which substance decomposes With releaseof gaseous decomposition product therefrom when said sheet is heated todry the gum coating thereon and whereby the released gas effectsfracturing of the dried gum coating on the sheet.

14. A coating batch according to claim 13, wherein said gas-providingsubstance is a member of the class consisting of oxybis benzenesulfonylsemicarbazide, oxybis benzenesulfonyl hydrazide, azodicarbonamide,trihydrazino-sym-triazine, dimethyl dinistrosoterephthalamide, bariumazodicarboxylate, and bis-benzenesulfonyl hydrazide.

15. A coating batch as claimed in claim 14, wherein the gas-providingsubstance is azodicarbonamide.

16. A gummed sheet comprising a backing of porous material andadhesively attached thereto a fractured dried coating of a moistenableadhesive, which coating of said frangible dried moistenable adhesive hasa multiplicity of fracture lines in an irregular array exhibitingsubstantially negligible recurrent pattern; said gummed sheet beingsubstantially free of any tendency to become dimensionally distortedwhen moistened and subjected to drying heat and in contrast to, andwhich tendency so to be distorted is manifested by, a correspondinggummed sheet having such backing and attached to it a continuous driedcoating of said adhesive, with said coating being free of fracturelines.

17. A gummed sheet according to claim 16, in which the number offracture lines in the dried coating is many times greater per unit areathan the fracture lines produced by a conventional mechanical breakingoperation. 18. A laminated fibrous stock sheet product comprising aplurality of sheets of fibrous stock bonded together at their adjacentfaces by an intervening dried adhesive layer having a multiplicity offracture lines occuring in random array exhibiting substantiallynegligible recurrent pattern.

References Cited by the Examiner UNITED STATES PATENTS 1,148,783 8/1915Knappstein 117-11 1,958,721 5/ 1934 Scott 117-11 2,770,406 11/ 1956Lane.

2,815,297 12/ 1957 Herrlinger 117-11 2,849,332 8/1958 Smith et a1 117-412,947,647 8/ 1960 Hart et a1 117-11 2,973,295 2/1961 Rogers.

3,041,193 6/1962 Hamway et al. 117-11 EARL M. BERGERT, Primary Examiner.

J. F. BURNS, T. R. SAVOIE, Assistant Examiners.

18. A LAMINATED FIBROUS STOCK SHEET PRODUCT COMPRISING A PLURALITY OFSHEETS OF FIBROUS STOCK BONDED TOGETHER AT THEIR ADJACENT FACES BY ANINTERVENING DRIED ADHESIVE LAYER HAVING A MULTIPLICITY OF FRACTURE LINESOCCURING IN RANDOM ARRAY EXHIBITING SUBSTANTIALLY NEGLIGIBLE RECURRENTPATTERN.